Single crystals, method for making single crystals by growth in solution and uses

ABSTRACT

The invention relates to a tetragonal single crystal ( 1, 11 ) of composition:  
     Z(H,D) 2 MO 4    
     where Z is an element or a group of elements, or a mixture of elements and/or of groups of elements chosen from the group K, N(H,D) 4 , Rb, Ce  
     where M is an element chosen from the group P, As and where (H,D) is hydrogen and/or deuterium  
     comprising an approximately parallelepipedal region of large dimensions, especially one in which the length of each of the edges of the faces, AC1, AC2, AC3, is greater than or equal to 200 mm, in particular greater than or equal to 500 mm, which crystal is obtained by crystal growth from solution, from an approximately parallelepipedal single-crystal seed ( 2, 22 ) whose edges of the faces have lengths of AG1, AG2, AG3.  
     According to the invention, at least the length of one edge, AG1, of the seed is greater than or equal to one tenth, preferably one quarter, of the length of one edge of the faces of the single crystal and at least one other length of the seed, AG3, is less than or equal to one fifth, preferably one tenth, of the greatest length of the edges of the faces of the seed.  
     The invention also relates to the process which allows such tetragonal single crystals to be obtained.  
     Such single crystals are particularly beneficial for obtaining optical components, especially for laser applications.

[0001] The invention relates to the field of single crystals and moreparticularly to large tetragonal single crystals. It also relates to agrowth process for obtaining said single crystals and to a process formanufacturing single-crystal plates obtained from the single crystalsmanufactured by the growth method. It also relates to the applicationsand uses of said single-crystal plates, especially as opticalcomponents, in particular as laser components.

[0002] Crystals of the type of those of the invention have beenespecially developed to meet the demands of high-power lasermanufacturers who require large optical components.

[0003] This is because, in the context of research on nuclear fusion byinertial confinement, projected lasers require the production of largeKDP (potassium dihydrogen phosphate, KH₂PO₄) single crystals. Thesecrystals are used either as an optical switch (in the form of a Pockelscell) or as a frequency doubler or tripler for the light emitted by thelaser source. It is also possible to use crystals of deuteratedpotassium phosphate or DKDP.

[0004] Further crystal compositions are presently being studied.

[0005] The crystals, especially KDP crystals, are produced in the formof boules from which plate-shaped pieces are cut, which will thus beused in the apparatuses in question. In the case of a Pockels cell, aplate cut perpendicular to the Z axis of the crystal is used. In thecase of a frequency multiplier, the plate is cut in well defineddirection, known to those skilled in the art. For example, for afrequency doubler a plate is cut which has its large face lying in aplane at 41° to the XY plane and which cuts this XY plane at pointsequidistant from the origin along the X axis and along the Y axis, asmay be seen in FIG. 4, and, for a frequency tripler, a plate is cutwhich has its large face lying at 59° to the XY plane and which cutsthis XY plane along a line parallel to the X axis, as may be seen inFIG. 5.

[0006] Known methods for growing large tetragonal single crystals aredescribed, for example, in the publication by Zaitseva et al., “Rapidgrowth of large-scale (40-55 cm) KH₂PO₄ crystals”, Journal of CrystalGrowth 180 (1997), 255-262.

[0007] Large-scale tetragonal single crystals are understood to meansingle crystals in which each of the edges of the faces, denoted AC1,AC2, AC3, have a length greater than or equal to 100 mm, especiallygreater than or equal to 200 mm and even, in particular, greater than orequal to 500 mm.

[0008] In the above publication, crystals of this type are obtained bygrowth from solution, from a point seed, that is to say a single crystalwhose size is small compared with the size of the crystal that it isdesired to obtain, especially with a seed size of the order of 1 cm³.Furthermore, the lengths of the edges of the seed are all approximatelyequal. In this technique, and using a supersaturated solution asdescribed in the publication, it is possible to obtain a tetragonalcrystal about 450 mm in length in the X, Y and Z directions in 30 days.This method will hereafter be referred to as the “reference method”.

[0009] This technique, although having been the first to allow themanufacture of large-scale tetragonal single crystals, has severaldrawbacks.

[0010] This is because with the ever increasing power of lasers, thesize of the desired optical components increases, and it is now desiredto obtain plates for laser components two of whose dimensions aregreater than 400 mm. This requires the production of boules having atleast a base of 600 mm per side and of sufficiently large height toextract the desired plates.

[0011] It is conceivable to increase the size of the apparatus in whichthe crystals grow. However, this increase in size comes up againsttechnical problems difficult to solve. This is because, as describedbelow, growth takes place from the solution contained in a crystallizer,generally made of glass. However, it becomes very expensive to obtaincrystallizers of large size, especially having a diameter of more thanone meter, and it is necessary to have a very large volume of solution.Another technical problem relates to the fact that, to increase the sizeof the crystals with the reference method it is necessary to increasethe growth time. This increase in the growth time can lead to defectshighly damaging for the crystals obtained, since the probability ofdeveloping spurious crystals from seeds in the solution or from the freesurfaces of the growth apparatus, which surfaces may constitute seeds,considerably increases with the growth time.

[0012] Furthermore, the extraction yield, defined as being the ratio ofthe volume of plates useful as optical components to the volume of theboule from which they are extracted with the reference method, isgenerally low, often of the order of 10%.

[0013] The object of the present invention is to remedy theabovementioned drawbacks, especially by making it possible to increasethe extraction yield of the plates used as optical components extractedfrom a boule, while continuing to use growth apparatuses of reasonablesize which allow, in particular, the volume of solution needed forgrowing a boule to be limited.

[0014] The problem of obtaining a single-crystal boule with a growthapparatus of reasonably large size, from which a large number of platescan be extracted, is solved by the use of a seed of particular shape anddimensions.

[0015] One subject of the present invention is a tetragonal singlecrystal of composition:

Z(H,D)₂MO₄

[0016] where Z is an element or a group of elements, or a mixture ofelements and/or of groups of elements chosen from the group K, N(H,D)₄,Rb, Ce

[0017] where M is an element chosen from the group P, As and

[0018] where (H,D) is hydrogen and/or deuterium

[0019] comprising an approximately parallelepipedal region of largedimensions, especially one in which the length of each of the edges ofthe faces, AC1, AC2, AC3, is greater than or equal to 200 mm, inparticular greater than or equal to 500 mm, which crystal is obtained bycrystal growth from solution, from an approximately parallelepipedalsingle-crystal seed whose edges of the faces have lengths of AG1, AG2,AG3, where at least the length of one edge, AG1, of the seed is greaterthan or equal to one tenth, preferably one quarter, of the length of oneedge of the faces of the single crystal and where at least one otherlength of the seed, AG3, is less than or equal to one fifth, preferablyone tenth, of the greatest length of the edges of the faces of the seed.

[0020] This tetragonal single crystal may serve as a boule from whichsingle-crystal plates will be cut.

[0021] This tetragonal single crystal may especially be of compositionKH₂PO₄(known by the abbreviation KDP), K(H,D)₂PO₄ (DKDP, that is to saydeuterated KDP), (NH₄)H₂PO₄ (ADP) and N(H,D)₄(H,D)₂PO₄ (DADP ordeuterated ADP).

[0022] It is also possible to obtain crystals of composition Rb(H,D)PO₄and CE(H,D)PO₄ (deuterated or nondeuterated).

[0023] We should point out that, for some applications, it is beneficialto use substitutions or mixtures based on elements or associated groupsof elements from K, N(H,D)₄, Rb, and Ce.

[0024] Crystals having the same structure can also be obtained byreplacing P with As for all the abovementioned compositional variants ofthe crystal.

[0025] It is thus possible to define the “KDP family” as described inthe work “KDP—a family of single crystals” by L. N. Rashkovich (AdamHilger IOP Publishing Limited, 1991) and especially as noted, forexample, in the following publications: Landolt-Börnstein, 1984(Numerical Data and Functional Relationships in Science and Technology,New Series, Vol. 18—suppl. to vol. III/11, edited by K -H Hellwege andA. M. Hellwege, published by Springer, Berlin), D. Eimerl, 1987 (1987a“Electro optic, linear and nonlinear optical properties of KDP and itsisomorphs”, Ferroelectrics, 72, 95-130 and 1987b “High average powerharmonic generation”, IEEE J. Quantum Electron., QE-23 575-92) and E.Courtens, 1987 (“Mixed crystals of the KH₂PO₄ family”,Ferroelectrics,72, 229-44).

[0026] It is known that a tetragonal crystal is composed of anapproximately parallelepipedal region and at least one of these facesmay be extended by a pyramid, the edges of the base of which correspondto the edges of said face.

[0027] According to a preferred embodiment of the invention, the seed isa rod, the two lengths of the shortest edges of which, AG2, AG3, areapproximately equal to each other and less than or equal to one fifth,preferably one tenth, of the length of the longest edge, AG1, of therod.

[0028] The expression “approximately equal lengths” is understood hereand in the rest of the text to mean lengths which are of the same orderof magnitude, especially where one length is at most twice the other.

[0029] According to another embodiment of the invention, the seed is aplate, the lengths of the two longest edges of which, AG3, AG1, areapproximately equal to each other and greater than or equal to fivetimes, preferably ten times, the length of the shortest edge, AG2, ofthe plate.

[0030] According to an advantageous variant of the invention, thesingle-crystal seed is a tetragonal single crystal of composition:

Z (H,D)₂MO₄

[0031] where Z is an element or a group of elements, or a mixture ofelements and/or of groups of elements chosen from the group K, N(H,D)₄,Rb, Ce

[0032] where M is an element chosen from the group P, As and

[0033] where (H,D) is hydrogen and/or deuterium.

[0034] According to one embodiment of the invention, the tetragonalsingle crystal that can be especially used as a boule, from which platesof single crystals are cut, and the single-crystal seed have the samechemical composition.

[0035] The invention also relates to a process for manufacturing atetragonal single crystal by growth from solution, from an approximatelyparallelepipedal single-crystals seed, the edges of the faces of whichhave lengths of AG1, AG2 and AG3, which is supported on a platformimmersed in the solution and set in rotation, said single crystal havinggrowth rates (Vx, Vy, Vz) of the same order of magnitude along theprincipal crystallographic axes (X, Y, Z), especially where the slowestgrowth rate is greater than or equal to one quarter, especially onehalf, of the fastest growth rate, which process comprises at least thefollowing steps:

[0036] the seed is cut from a single crystal so that at least one lengthof the edges, AG3, of the seed is less than or equal to one fifth,preferably one tenth, of the geatest length of the edges of the seed,AG1, and so that at least one length of the edges of the seed is greaterthan or equal to 25 mm, especially greater than or equal to 50 mm;

[0037] the seed is positioned on the platform in the desiredorientation; and

[0038] the platform with the seed is put into a crystallizer containingthe solution and then set in rotation, in order to carry out the growthof the single crystal.

[0039] This manufacturing process makes it possible to obtain largesingle crystals which can be used as boules from which plates of singlecrystals will be cut.

[0040] The single-crystal seed may be cut, for example, either from asingle crystal obtained according to a known growth method or from asingle crystal grown beforehand using the abovementioned method.

[0041] It is known to those skilled in the art that the characteristicsof a tetragonal crystal are defined by the crystallographic axes X, Y,Z. The growth rate of the faces of this crystal along the X, Y, Z axisare called Vx, Vy, Vz, respectively.

[0042] According to a preferred embodiment, the seed is placed so thatthe growth axes X, Y, Z coincide with those of the edges of the seed.

[0043] According to a preferred variant of the invention, the seed usedin the process below is a rod, the lengths of the two shortest edges ofwhich, AG2, AG3, are approximately equal to each other and less than orequal to one fifth, preferably one tenth, of the length of the longestedge, AG1, of the rod.

[0044] A single crystal, able to be used as a boule, at least twodimensions of which are substantially equal, is thus obtained.

[0045] According to another variant of the process according to theinvention, the seed is a plate, the lengths of the two longest edges ofwhich, AG3, AG1, are approximately equal to each other and greater thanor equal to five times, preferably ten times, the length of the shortestedge, AG2, of the plate.

[0046] A single crystal that can be used as a boule, at least onedimension of which is less than the other two, is therefore obtained.

[0047] The latter two variants are cited as preferred examples ofimplementation, but variants should not be excluded in which the seedhas an intermediate configuration between a rod and a plate.

[0048] According to one method of implementing the process according tothe invention, the single-crystal seed is a tetragonal single crystal ofcomposition:

Z(H,D)₂MO₄

[0049] where Z is an element or a group of elements, or a mixture ofelements and/or of groups of elements chosen from the group K, N(H,D)₄,Rb, Ce

[0050] where M is an element chosen from the group P, As and

[0051] where (H,D) is hydrogen and/or deuterium.

[0052] According to one way of implementing the process according to theinvention, the tetragonal single crystal obtained by growth fromsolution has the same chemical composition as the single-crystal seed.

[0053] According to an advantageous variant of the process according tothe invention, the solution is supersaturated, especially with asupersaturation a of between 0.1% and 20%.

[0054] The notion of supersaturation is known to those skilled in theart and defined, for example in the abovementioned article by Zaitsevaet al, as: $\sigma = \frac{C - C_{0}}{C_{0}}$

[0055] where C corresponds to the concentration of the solution

[0056] and C₀ corresponds to the equilibrium concentration of thesolution.

[0057] It should be noted that the preferred supersaturation range canbe divided into two particularly advantageous subranges:

[0058] firstly, a low supersaturation range, especially for a between0.1 and 0.5%, which results in slow growth of the crystals and makes itpossible to obtain crystals of remarkable optical quality and secondly,a high supersaturation range, especially for σ between 1 and 20%, andmakes it possible to obtain high growth rates.

[0059] According to one method of implementing the process according tothe invention, the single crystal obtained is of composition:

Z(H,D)₂MO₄

[0060] where Z is an element or a group of elements, or a mixture ofelements and/or of groups of elements chosen from the group K, N(H,D)₄,Rb, Ce

[0061] where M is an element chosen from the group P, As and

[0062] where (H,D) is hydrogen and/or deuterium.

[0063] It should be noted that it may be advantageous to use a seedhaving a composition different from that of the single crystal that itis desired to obtain.

[0064] For example, a KDP seed may be used in order to grow a DKDPcrystal.

[0065] Other configurations are possible, as long as the chemical andcrystallographic compatibility between the seed and the crystal ismaintained.

[0066] The invention also relates to a process for manufacturing atleast one tetragonal single crystal, in which a single crystal obtainedusing the process described above, called a boule, is used and in whichat least one single-crystal plate is cut from a region sufficiently farfrom the seed and from the regeneration region in order to obtainoptical properties allowing the plate(s) to be used as a lasercomponent.

[0067] The term “regeneration region” refers to the region around theseed, corresponding to a first growth phase of the crystal from theseed, especially to the pyramid which forms on the face perpendicular tothe Z axis of the seed and to a region, contiguous with the faces of theseed, which may be estimated to be in general 20% of the shortest lengthof the seed.

[0068] The crystal plates thus obtained are of excellent optical qualityand can be especially used for laser applications, particularly asPockels cells, or as a frequency doubler or frequency tripler dependingon the orientation of the cut made in the boule.

[0069] Further advantageous details and features of the invention willbecome apparent below from the description of illustrative examples ofthe invention, with reference to the appended figures which show:

[0070]FIG. 1: a perspective view of a single crystal according to theinvention, obtained from a “rod seed”;

[0071]FIG. 2: a perspective view of a single crystal according to theinvention, obtained from a “plate seed”;

[0072]FIG. 3, a sectional view of an apparatus suitable for the methodof growing a single crystal according to the invention;

[0073]FIG. 4: a view of a single crystal according to the invention andof the region from which a single crystal usable as a frequency doublercan be cut:

[0074]FIG. 4.1: a sectional view

[0075]FIG. 4.2: a top view;

[0076]FIG. 5: a view of a single crystal according to the invention andof the region from which a single crystal usable as a frequency triplercan be cut:

[0077]FIG. 5.1: a sectional view

[0078]FIG. 5.2: a top view

[0079]FIG. 1 shows a perspective view of a single crystal according tothe invention. The single crystal 1 is composed of a parallelepiped, theedges of the faces of which have, as lengths, AC1, AC2 and AC3, the saidparallelepiped being topped by a pyramid 4. The figure shows the seed 2from which the single crystal 1 was grown. This seed 2 is shown in solidlines in order to make the drawing easier to understand, although itlies at the core of the single crystal 1, with a lower face on the sameplane as the lower face of the single crystal 1. This seed 2 is aparallelepiped, the two edges AG2 and AG3 of which are of much smallerlength than the edge AG1. According to the invention AG2 and AG3 areless than or equal to one fifth, or even one tenth, of AG1. The seed isthen referred to as a “rod seed”.

[0080] It should be noted that, in the case of the crystals according tothe invention, it is generally possible to visually detect the presenceand the dimensions of the seed 2 in the crystal 1 which has been grown.This is because crystals of the family of Z(H,D)₂MO₄ compositions, asdefined above, are transparent in the visible and/or ultraviolet and/orinfrared range and there are slight optical defects at the border of thefaces of the seed 2 in the crystal 1 which make it possible tocharacterize, unambiguously, the seed 2 from which the crystal wasgrown.

[0081]FIG. 2 shows a perspective view of another single crystalaccording to the invention. The considerations made above in regard toFIG. 1 also apply to FIG. 2. The difference between the crystal in FIG.1 and that in FIG. 2 relates to the shape of the seed used. The seed 22in FIG. 2 is a parallelepiped, the edges AG1 and AG3 of which are longerthan the edge AG2. The seed is then referred to as a “plate seed”.According to the invention, the longest two edges AG1 and AG3 have alength greater than or equal to five times, or even ten times, that ofthe edge AG3. The single crystal 11 obtained from this seed 22 comprisesa parallelepiped, the length of the edge AC3 of which is very muchgreater than that of the edge AC2.

[0082]FIG. 3 shows the cross section through an apparatus suitable forimplementing the process according to the invention. This apparatuscomprises a crystallizer 70 in which a solution 60 may be introduced. Aplatform 50, the size of which is generally slightly greater than thatof the single crystal 1, 11 that it is desired to obtain, is used. Thisplatform 50 is immersed in the solution 60 and rotated during the growthprocess. A seed 2, 22 is placed on the lower part of the platform. Thisseed 2, 22, shown here in cross section, may especially have the shapeof a rod or a plate, as defined above.

[0083] In general, the seed 2, 22 is placed so that its edges correspondto the crystallographic axes X, Y, Z. In the case shown in FIG. 3, theseed 2, 22 is placed so that one of these long lengths lies along the Zaxis and one of its short lengths along the X axis. This arrangement isin no way limiting and it is possible, depending on the crystals that itis desired to obtain, to place, for example, a long length of the seed2, 22 along the X axis or the Y axis.

[0084] This arrangement is particularly advantageous as it allows largecrystals to be rapidly obtained. This is because the crystals accordingto the invention have growth rates Vx, Vy, Vz of the same order ofmagnitude along the crystallographic axes X, Y, Z.

[0085] Let us consider an average growth rate V and compare the resultsobtained with those obtained from a conventional point seed. A pointseed is a parallelepiped which has each edge approximately of the samelength and which corresponds, for example, approximately to the lengthAG3 shown in FIG. 3.

[0086] Under these conditions, using a point seed, after a time t acrystal is obtained which has edges of the base in contact with theplatform 50 each of length AG3+2 Vt and a total height of AG3+Vt.

[0087] With the process according to the invention, after the same timet a crystal is obtained which has edges of the base in contact with theplatform 50 of length AG3+2 Vt and AG2+2 Vt and a height of AG1+Vt.

[0088] In this way, a crystal of significantly greater height isobtained with the process according to the invention than with theconventional process starting from a point seed. Likewise, it ispossible to obtain a lenth of one edge of the base which is very long,if it is chosen to use a plate seed.

[0089] Crystals can thus be obtained whose geometry makes it possible tocut a much larger number of plates for optical components than with thereference method, assuming that the single crystals were grown using anequivalent apparatus and under the same growth conditions.

[0090] In some cases, as the examples which follow illustrate, it ispossible to obtain at least ten times more plates from a crystalaccording to the invention than from a crystal obtained using thereference method.

[0091] The extraction yield is considerably increased, especially by afactor of at least three.

[0092] This results in substantial manufacturing cost savings.

[0093] It should be noted that the growth rate of the crystal may becontrolled by varying the supersaturation parameter σ of the solution60. The higher this parameter, the more rapid the growth.

[0094] It is possible to cut single-crystal plates usable as opticalcomponents from the crystals obtained.

[0095] This cutting is carried out in the volume of the crystal 1, 11,away from the volume of the seed 2, 22 and away from a regenerationregion 3 which lies in the immediate vicinity of the faces of the seed2, 22.

[0096]FIG. 4 shows a single crystal 1 according to the invention,illustrating the region from which a single-crystal plate 100 usable asa frequency doubler can be cut.

[0097] In the case shown, a rod seed 2 was used to grow the crystal 1.Other seeds, as defined according to the invention, may also be used.

[0098]FIG. 4.1 shows a cross section of the single crystal 1, in whichthe seed 2 surrounded by the regeneration region 3 may be seen. FIG. 4.2shows a top view in which the plate is depicted in solid lines in orderto make the figure easier to understand, with its hidden edge in abroken line. To obtain a plate 100 usable as a frequency doubler, a cutis made in a plane at 41° to the XY plane and intersecting the XY planeat points equidistant from the origin along the X axis and along the Yaxis. A plate 100 of lengths a, b, c is thus obtained.

[0099]FIG. 5 shows a single crystal 1 according to the invention fromwhich a plate 200 usable as a frequency tripler may be cut. Thenonlimiting considerations and conditions made with regard to FIG. 4apply to FIG. 5. To obtain a plate 200 usable as a frequency tripler, acut is made in a plane at 59° to the XY plane and intersecting this XYplane along a line parallel to the X axis.

[0100] To illustrate the advantages of the crystals and of the processesaccording to the invention, a comparative example will be described.

[0101] The crystal obtained under identical growth conditions, with thesame apparatus and the same solution, according to the reference methodand according to the teachings of the invention will be compared.

[0102] An apparatus comprising a glass crystallizer one meter indiameter and a platform 850 mm in diameter is used.

[0103] As mentioned above, these elements of the apparatus havedimensions which can be exceeded, but which would result in verysubstantial additional costs.

[0104] With such a platform, it is possible to obtain crystals with asquare base having sides of greater than 600 mm.

[0105] A supersaturated KDP solution is used, which results in thefollowing growth rates:

[0106] V_(vertical)=V_(z)=9 mm/day

[0107] V_(horizontal)=V_(x)=V_(y)=6 mm/day

[0108] The growth rates may vary by about 10%.

[0109] Example Ex1, according to the reference method, is that of acrystal obtained from a 10×10×10 mm³ point seed.

[0110] Example Ex2, according to the invention, is that of a crystalobtained from a 10×10×150 mm³ rod seed placed with its smallest face incontact with the platform.

[0111] Under these conditions, the horizontal growth rate of the twocrystals is identical and the maximum size is reached after 50 days.

[0112] After this time, the Ex1 crystal has a height of 450 mm and theEx2 crystal has a height of 600 mm.

[0113] This difference is extremely important as it allows many moreuseful crystals to be extracted from Ex2 than from Ex1.

[0114] In point of fact, in the practical case of the French power laserproject MEGAJOULE, frequency doublers having at least a=405 mm, b=420mm, c=12 mm have to be obtained. It is possible to extract, fromcrystals obtained according to Ex1 and taking into account thedimensional variations, one such frequency doubler plate in only aboutone Ex1 crystal in three. It is therefore necessary to wait on average150 days in order to obtain such a frequency doubler plate using thereference method.

[0115] It is possible to extract between 5 and 7 frequency doublerplates defined above from a crystal obtained according to Ex2. Thus, itis possible according to the invention to obtain at least 15 doublerplates in the period of 150 days needed to obtain a single plateaccording to the reference method.

[0116] An equivalent comparison may be developed for obtaining frequencytripler plates of the same size as the above frequency doublers.

[0117] It should be noted that, thanks to the teaching of the invention,it is possible to obtain a large number of plates for components, whilekeeping reasonable dimensions of the growth apparatus, and that thisvery substantial increase in the number of plates coming from a boule isobtained by a moderate increase in the height of the boule (an increasein height of about one third). Thus, very advantageous savings ofmaterial are obtained, since at best about 10% of the volume of theboule can be exploited with the reference method, whereas more than 30%of the volume of the boule can be exploited with the method according tothe invention.

[0118] The comparison between these examples clearly demonstrates theconsiderable increase in useful volume for cutting plates, and thereforean equivalent increase in the production yield of plates usable asoptical components, that the invention allows.

[0119] The invention is not limited to these particular embodiments andmust be interpreted in a nonlimiting manner as encompassing anytetragonal single crystal of composition:

Z(H,D)₂MO₄

[0120] where Z is an element or a group of elements, or a mixture ofelements and/or of groups of elements chosen from the group K, N(H,D)₄,Rb, Ce

[0121] where M is an element chosen from the group P, As and

[0122] where (H,D) is hydrogen and/or deuterium

[0123] comprising an approximately parallelepipedal region of largesize, especially one in which the length of each of the edges of thefaces, AC1, AC2, AC3, is greater than or equal to 200 mm, in particulargreater than or equal to 500 mm, obtained by crystal growth fromsolution, from an approximately parallelepipedal single-crystal seed (2,22), the edges of the faces of which have lengths of AG1, AG2, AG3,characterized in that at least the length of one edge, AG1, of the seedis greater than or equal to one tenth, preferably one quarter, of thelength of one edge of the faces of the single crystal and that at leastone other dimension of the seed, AG3, is less than or equal to onefifth, preferably one tenth, of the greatest length of the edges of thefaces of the seed.

[0124] The invention also relates to the growth process which allowssuch crystals to be obtained, but which can be used nonlimitingly togrow any tetragonal single crystal whose growth rates are of the sameorder of magnitude along the principal crystallographic axes.

[0125] The preferred crystals are those of the “KDP family”.

1. A process for manufacturing a tetragonal single crystal (1, 11) bygrowth from solution, from an approximately parallelepipedalsingle-crystal seed (2, 22), the edges of the faces of which havelengths of AG1, AG2 and AG3, which is supported on a platform (50)immersed in the solution (60) and set in rotation, said single crystal(1, 11) having growth rates (Vx, Vy, Vz) of the same order of magnitudealong the principal crystallographic axes (X, Y, Z), characterized inthat it comprises at least the following steps: the seed is cut from asingle crystal so that at least one length of the edges, AG3, of theseed is less than or equal to one fifth of the greatest length of theedges of the seed, AG1, and so that at least one length of the edges ofthe seed is greater than or equal to 25 mm, the seed is positioned onthe platform (50) in the desired orientation; and the platform (50) withthe seed (2, 22) is put into a crystallizer (70) containing the solution(60) and then set in rotation, in order to carry out the growth of thesingle crystal (1, 11).
 2. The process as claimed in the precedingclaim, characterized in that the growth rates (Vx, Vy, Vz) are such thatthe slowest growth rate is greater than or equal to one quarter of thefastest growth rate.
 3. The process as claimed in the preceding claim,characterized in that the slowest growth rate is greater than or equalto one half of the fastest growth rate.
 4. The process as claimed in oneof the preceding claims, characterized in that at least one length ofthe edges, AG3, of the seed is less than or equal to one tenth of thelongest edge, AG1, of the seed.
 5. The process as claimed in one of thepreceding claims, characterized in that at least one length of the edgesof the seed is greater than or equal to 50 mm.
 6. The process as claimedin one of the preceding claims, characterized in that the seed is a rod(2), the lengths of the two shortest edges of which, AG2, AG3, areapproximately equal to each other and less than or equal to one fifth ofthe length of the longest edge, AG1, of the rod.
 7. The process asclaimed in one of the preceding claims, characterized in that thelengths of the two smallest edges, AG2, AG3, are approximately equal toeach other and less than or equal to one tenth of the length of thelongest edge, AG1, of the rod.
 8. The process as claimed in one ofclaims 1 to 6, characterized in that the seed is a plate (22), thelengths of the two longest edges of which, AG3, AG1, are approximatelyequal to each other and greater than or equal to five times the lengthof the shortest edge, AG2, of the plate.
 9. The process as claimed inthe preceding claim, characterized in that the lengths of the twolongest edges, AG3, AG1, are approximately equal to each other andgreater than or equal to ten times the length of the smallest edge, AG2,of the plate.
 10. The process as claimed in one of the preceding claims,characterized in that the single-crystal seed (2, 22) is a tetragonalsingle crystal of composition Z(H,D)₂MO₄, where Z is an element or agroup of elements, or a mixture of elements and/or of groups of elementschosen from the group K, N(H,D)₄, Rb, Ce, where M is an element chosenfrom the group P, As and where (H,D) is hydrogen and/or deuterium. 11.The process as claimed in one of the preceding claims, characterized inthat the tetragonal single crystal (1, 11) obtained by growth fromsolution has the same chemical composition as the single-crystal seed(2, 22).
 12. The process as claimed in one of the preceding claims,characterized in that the solution is supersaturated, especially with asupersaturation σ of between 0.1% and 20%.
 13. The process as claimed inone of the preceding claims, characterized in that the single crystal(1, 11) obtained is of composition Z(H,D)₂MO₄, where Z is an element ora group of elements, or a mixture of elements and/or of groups ofelements chosen from the group K, N(H,D)₄, Rb, Ce, where M is an elementchosen from the group P, As and where (H,D) is hydrogen and/ordeuterium.
 14. The process as claimed in the preceding claim,characterized in that the single crystal comprises an approximatelyparallelepipedal region of large size, especially one in which thelength of each of the edges of the faces, AC1, AC2, AC3, is greater thanor equal to 500 mm.
 15. A process for manufacturing at least onetetragonal single crystal (100, 200), characterized in that a singlecrystal (1, 11) obtained using the process as claimed in one of thepreceding claims is used and in that at least one single-crystal plate(100, 200) is cut from a region sufficiently far from the seed (2, 22)and from the regeneration region (3) in order to obtain opticalproperties allowing the plate(s) (100, 200) to be used as a lasercomponent.
 16. A single crystal that can be obtained by the process ofone of the preceding claims.
 17. A tetragonal single crystal (1, 11) ofcomposition Z(H,D)₂MO₄, where Z is an element or a group of elements, ora mixture of elements and/or of groups of elements chosen from the groupK, N(H,D)₄, Rb, Ce, where M is an element chosen from the group P, Asand where (H,D) is hydrogen and/or deuterium comprising an approximatelyparallelepipedal region of large size, especially one in which thelength of each of the edges of the faces, AC1, AC2, AC3, is greater thanor equal to 100 mm, obtained by crystal growth from solution, from anapproximately parallelepidedal single-crystal seed (2, 22) whose edgesof the faces have lengths of AG1, AG2, AG3, characterized in that atleast the length of one edge, AG1, of the seed is greater than or equalto one tenth, preferably one quarter, of the length of one edge of thefaces of the single crystal and in that at least one other length of theseed, AG3, is less than or equal to one fifth, preferably one tenth, ofthe greatest length of the edges of the faces of the seed.
 18. Thesingle crystal as claimed in the preceding claim, characterized in thateach of the edges of the faces, AC1, AC2, AC3, is greater than or equalto 200 mm.
 19. The single crystal as claimed in the preceding claim,characterized in that each of the edges of the faces, AC1, AC2, AC3, isgreater than or equal to 500 mm.
 20. The single crystal (1) as claimedin one of claims 17 to 19, characterized in that the seed is a rod (2),the two lengths of the shortest edges of which, AG2, AG3, areapproximately equal to each other and less than or equal to one fifth,preferably one tenth, of the length of the longest edge, AG1, of therod.
 21. The single crystal (11) as claimed in one of claims 17 to 19,characterized in that the seed is a plate (22), the lengths of the twolongest edges of which, AG3, AG1, are approximately equal to each otherand greater than or equal to five times, preferably ten times, thelength of the shortest edge, AG2, of the plate.
 22. The single crystalas claimed in one of claims 17 to 21, characterized in that thesingle-crystal seed (2, 22) is a tetragonal single crystal ofcomposition Z(H,D)₂MO₄, where Z is an element or a group of elements, ora mixture of elements and/or of groups of elements chosen from the groupK, N(H,D)₄, Rb, Ce, where M is an element chosen from the group P, Asand where (H,D) is hydrogen and/or deuterium.
 23. The single crystal (1,11) as claimed in the preceding claim, characterized in that the singlecrystal (1, 11) and the single-crystal seed (2, 22) have the samechemical composition.
 24. The use of a single-crystal plate obtained bythe process of claim 15 as a Pockels cell.
 25. The use of asingle-crystal plate (100) obtained by the process of claim 15 as afrequency doubler.
 26. The use of a single-crystal plate (200) obtainedby the process of claim 15 as a frequency tripler.